1. Field of the Invention
This invention relates generally to the structure and fabrication process of the integrated circuits (ICs). More particularly, this invention relates to the structure and fabrication process of implementing the inductive circuits as part of the integrated circuits (ICs) which have line-width in the range of a micron or sub-mircons such the the inductive circuit can be fully integrated and be regularly employed as an IC circuit element.
2. Description of the Prior Art
Even though the electronic circuits are continuously being miniaturized through the progress made in the very large system integration (VLSI) and the ultra-large system integration (ULSI) fabrication technology, the integrated circuit (IC) technology is yet limited by a great difficulty that the inductive circuits are still not suitable for IC implementation. This difficulty arises due to the fact that the IC fabrication techniques are mostly `layer-oriented` which typically involve processes which are applied to multiple horizontal surfaces in a sequential fashion. However, the inductive circuit has a `non-planar` configuration which typically has a continuous spiral shape. This particular non-planar configuration thus prevents the IC fabrication process to integrate the inductive circuits as part of the IC devices.
This technical difficulty severely limits the application scope of the IC technology. The inductive circuits are broadly used in various filters, oscillators, resonators, transformers, and many other control circuits for applications in communication signal generation and processing, energy storage, and electric static discharge (ESD) or electric over stress (EOS) protections. This limitation of not able to integrate the inductive circuit on an IC chip greatly hinders the technical progress in these fields. As will be discussed below, the traditional design and fabrication techniques for devices involve inductive circuits are still being applied without much progress for many decades. Such a difficulty further prevents all the devices which incorporate inductive circuits from being benefited from the IC fabrication technology. Thus the devices which requires the use of inductive circuits all tends to have large volume and more costly compared to the IC fabricated devices due to the facts that they cannot be miniaturized and mass-produced by the use of the highly precise and efficient IC fabrication technology.
In U.S. Pat. No. 4,783,646 entitled `Stolen Article Detection Tag Sheet, and Method for Manufacturing the Same` (issued on Nov. 8, 1988), Matsuzaki discloses a stolen article detection tag sheet. The tag sheet includes a transmitting antenna section, a receiving antenna section and an inductor section connected in series between the receiving and the transmitting antenna section. The tag sheet further includes a semi-conductor diode chip having a semiconductor substrate mounted on and electrically connected to a first portion of the inductor section and a Schottky barrier electrode formed on top of the substrate. The tag sheet further includes a second conductive pattern which is formed in contact with the conductive member of the Schttoky barrier electrode. The semiconductor chip diode and the inductor section are connected in parallel to each other to constitute an LC resonator and the frequency of the resonator is determined by the parasitic capacitance of the diode and the inductance which is 2.4 nH in this particular tag sheet.
Matzusaki discloses a method to implement an LC resonating circuit on a print circuit (PC) board. However, as Matzusaki's technique discloses a configuration to fabricate an LC circuit, wherein inductance is generated together with a parasitic capacitance by connecting a conductive line in parallel with the electrode of a diode, it does not teach a method to fabricate an inductor alone on the integrated circuit (IC) chips. Furthermore, since the size of the resonator as disclosed by Matzusaki is in the range of few hundred microns (.mu.m), the technique and device configuration disclosed by Matzusaki are not applicable for fabrication of IC devices with line width of few microns or in the sub-micron range.
In another U.S. Pat. No. 4,841,253 entitled `Multiple spiral Inductors for DC Biasing of An Amplifier` (issued on Jun. 20, 1989), Crabill discloses a monolithic semiconductor having an on-chip DC biasing which includes a plurality of series connected spiral inductors connected between respective biasing and the semi-conductor circuit. As shown in FIGS. 1, 2 and 3, the inductive means as claimed in this Patent, including these spiral inductors are external off-chip components. These type of inductive circuits, due to the particular configuration of expanding as a spiral on a horizontal plane, tend to occupy large IC chip areas and therefore not suitable for compact IC integration, especially for very large scale integration (VLSI). Furthermore, since the plane configuration, the inductance which can be provided by this flat spiral inductor is very limited. The application of the conductors as disclosed and used in Crabill's invention is therefore quite limited.
Other than the spiral inductors as discussed above, the state of the art in utilizing an inductive circuit in various devices can be illustrated by referencing to the U.S. Pat. No. 4,800,32, entitled `Single Ended Self-Oscillating DC-DC Converter for Intermittently Energized Load Having V.sub.BE Responsive Current Limit Circuit` (issued on Jan. 24, 1989) by Sikora, or another U.S. Pat. No. 4,845,580 entitled `AC DC Spike Eliminating Bandpass Filter` (issued on Jul. 4, 1989) by Kitchen. The inductive circuits as disclosed in these Patents are still introduced as wire-winding circuit components. These inductive circuits obviously cannot be implemented on an IC chip as part of an IC device.
Therefore, there is still a need in the art of IC device fabrication, particularly for the electronic devices which require the use of the inductive circuits, to provide a structure and fabrication process that would resolve these limitations.